1. Field of the Invention
The present invention relates to a method and an apparatus for determining the position of a pick-up head (PUH), more particularly to a method and an apparatus for correctly detecting the absolute position of the pick-up head along the radial direction of an optical storage medium to distinguish between the areas of the same address information thereon.
2. Description of the Related Art
FIG. 1 is a schematic diagram illustrating the information area structure of a quarter of a conventional optical storage medium. At the center of an optical storage medium 10 (for example, an optical disk like the CD-R format or the CD-RW format), there is a center hole 11 for a spindle of an optical storage device to synchronously rotate with the medium 10. The information area of the optical storage medium 10 is sequentially divided into a laser power calibration area (PCA) 12, a program memory area (PMA) 13, a lead-in (LI) area 14, a program area (PA) 15 and a lead-out (LO) area 16 from its interior to its exterior.
When the mold of a recordable optical storage medium is engraved with grooves, the shallow groove starts from the center of the optical storage medium and is spirally formed thereon by means of a laser beam controlled by a predetermined program. Known as a pre-groove, the groove does not look like a smooth spiral, but instead is a spiral that wobbles in a sinusoidal waveform of tiny amplitude. A signal read from the pre-groove is hereinafter referred to as a “wobble signal.” Every sector on an optical disk generally fabricated by die-casting contains time-related data for controlling the rotational speed of an optical storage device, in order to correctly read signals recorded on the optical disk.
It is necessary for a recordable optical storage device to guide the laser beam of the pick-up head to move outward in proper sequence and control its rotational speed correctly according to some means. Since the tracking and timing code information is provided by the wobbling pre-groove, such information is called ATIP (Absolute Time In Pre-groove) data. With the data, the recording speed of signals can be kept constant. To record data on a recordable optical disk, the optical storage device adds the address information to the main data, and then the combined data are encoded and scrambled before the processed main data converted by Eight-to-Fourteen Modulation (hereinafter referred to as “EFM signals”) are recorded on the tracks of the recordable optical disk. Later on, to retrieve the recorded data, the optical storage device demodulates the EFM signals first and then descrambles and decodes them in order to read the main data and address information. If the EFM signals burned to an optical disk are present, the optical storage device can use such signals to make the optical pick-up head move in proper sequence and control the rotational speed of a spindle motor. On the other hand, after the signals are successfully decoded, the physical address information required for the positioning of the pick-up head can be obtained.
FIG. 2 is a diagram illustrating the scheme of ATIP data. The ATIP data comprises a 4-bit sync code, an 8-bit minute (M) code, an 8-bit second (S) code, an 8-bit frame (F) code, and a cyclic redundancy check code (CRC). ATIP time codes {MM: SS: FF} can define the absolute beginning and the absolute destination of every sub area in an information area of an optical disk and are obtained through the minute codes, second codes, and frame codes; wherein MM, SS and FF denote the minute code (0-99), second code (0-59), and frame code (0-74), respectively.
FIG. 3 is a diagram illustrating the corresponding relationship between an information area and an ATIP time code. Referring to FIG. 3, t1 denotes the start time code of the laser beam power calibration area (PCA) 12, which is set to {95:00:00} in most optical disks, t2 denotes the start time code of the program memory area (PMA) 13, t3 denotes the start time code of the lead-in area (LI) 14, t4 may preferably denote the end time code {99:59:74} of the lead-in area (LI) 14 or the start time code {00:00:00} of the program area (PA) 15, and t5 denotes the last possible start time code of the lead-out area (LO) 16, for example, an 80-minute CD-R disk designates t5 as {79:59:74}.
At present, it is quite common for the program area (PA) 15 of an optical disk to have a capacity greater than 95 minutes, and in consequence it is impossible to map time codes one-to-one and onto the locations of the various areas in the optical disk, as shown in FIG. 4. Obviously, an interval of the time code from {95:00:00} to {99:59:74} can be mapped to two different areas, thus it is impossible to determine the exact position of the pick-up head, as far as its whereabouts is concerned, using the ATIP time code extracted from ATIP information; in other words, the exact position of the pick-up head is necessarily determined by an auxiliary means, such as other conditions or data.
FIG. 5 is a diagram about the structure of subcode-Q data in mode 1. An ADR (address) of 1h indicates mode 1, wherein h denotes a hexadecimal number. A TNO (track number) of 00h indicates that the subcode-Q data is stored at the lead-in area disposed in the innermost tracks. On the contrary, if the TNO is not equal to 00h, the corresponding subcode-Q data may be stored in a program area or a lead-out area. Hence, it is possible to determine the current position of the pick-up head by reading the information of the subcode-Q data with a logic program executed during tracking.
According to the way they are burned, optical disks are divided into two types, namely single-session and multi-session, as shown in FIGS. 6(a) and 6(b). A single-session optical disk 61 can be written once only and thus its data structure is simple; as a result, a TNO of 00h indicates that the subcode-Q data is stored in the lead-in area disposed in the innermost tracks. However, as for a multi-session optical disk 62, it is impossible to determine whether the pick-up head is currently located in a lead-in area (LI) between two program areas (PA) or in the innermost lead-in area (LI), even if the TNO equals 00h.
In general, predetermined functions of an optical disk drive, such as reading recorded data, writing data, reading data of a TOC (table of contents) from a lead-in area, and reading data of PMA, are achieved by the execution of various procedures which depend on the need, as far as the operation and application of the optical disk are concerned. However, for whatever functions to be executed, a seeking-and-tracking servo control circuit is always called first to move the pick-up as long as the functions attempt to read/write data from/to the optical disk. After the pick-up head moves to a target area, it executes extracting or writing data from or to the target area through following tracks. The mechanism of seeking is that the seeking-and-tracking servo control circuit reads the present address (acquired by means of the ATIP time code or the subcode-Q data) to confirm the “current position” first after a caller, such as a function which is attempting to read the data stored at the target position, gives a command of getting to a “target position”; then, the jumping direction and distance crossing the tracks are calculated in the light of the relationship between the current position and the target position, and the jumping action is executed in accordance with the result of the calculation. Track locking starts again when the seeking action is done, though it entails reading the present address once again in order to confirm whether the pick-up head reaches the target area. If the arrival of the pick-up head at the target area is confirmed, the seeking action ends; otherwise, the seeking action continues in the light of the relationship between the current position and the target position until the pick-up head reaches the predetermined target area.
In fact, the optical storage device is unable to determine the current position solely by means of the ATIP time code or the subcode-Q data, as it is still necessary to set an area flag which indicates that in or not in a specified area for determining some positions which correspond to overlapping time codes. When the optical storage device drives the pick-up head to get the positions of which time codes are in the time-code-overlap areas, the flag needs to be set for confirming which one of the positions is the target position before calling a seeking-and-tracking servo-control loop. During the process of seeking the target tracks, the seeking-and-tracking servo-control loop reads the address of the current position to determine the next seeking movement and confirm whether it is at the target position or not. If the current position read by the seeking-and-tracking servo-control loop is at the areas of the overlapping time codes, it is necessary to have additional criteria or information to assist the loop in confirming which one of the areas corresponds to the current position. Because seeking motion or tracking (following) motion possibly occurs in the areas of the overlapping time codes, it is necessary to refer to the past trajectory of the pick-up head, such as the direction and distance of the seeking motion and the proceeding distance of the tracking motion, for confirming which one of the areas corresponds to the current position. Hence, the data of the area flag have to be checked out or reset whenever a different application procedure is executed, and auxiliary conditions are continually renewed and judged in the light of variations in the positions of the pick-up head predicted by individual application procedures. Hence, program maintenance is difficult, while omissions are common, especially that the movements of pick-up head are different and complex for many kinds of purposes and operation sequences for optical devices; as a result, any ensuing judgment is indefinite. Furthermore, the complicated examination and configuration which are taking place in the area flag and auxiliary conditions inevitably decrease the execution efficiency of the entire system, not to mention that such an additional confirmation program has not been applied to all optical disks with different formats yet.